1. Field of Invention
This invention pertains generally to angular rate sensors or gyroscopes and, more particularly, to a dual mass rate sensor in which momentum is balanced and the drive and sense modes are decoupled.
2. Related Art
In rate sensors or gyroscopes, the use of two coupled proof masses which oscillate in an out-of-phase manner in the drive mode is a common way of balancing the drive momentum in order to minimize the transfer of energy to the substrate. In addition, with the masses being driven in an anti-phase manner, the response of the masses to Coriolis forces will also be out of phase, which allows the effects of external vibrations to be cancelled.
Out-of-phase oscillation in the drive mode is commonly achieved by coupling the two proof masses together with a spring, which has some significant disadvantages. The resulting dynamic system has two resonances—a parasitic in-phase mode and the desired out-of-phase mode, with the in-phase mode always being lower in frequency than the out-of-phase mode. In addition, imperfections in fabrication often result in the masses being of slightly different size, which prevents them from oscillating with equal amplitudes. The unequal oscillations produce an imbalance in momentum and result in undesired transfer of energy to the substrate.